Magical Math

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Imagine a world without aids“ is a slogan we don’t hear much anymore. But a decade ago, the arts community, shattered by the epidemic, seized upon it as an urgent message, plastering their visions of hope and healing -- or rage and resistance -- on a blood-soaked reality (see ”Visualize This" below). More recently, we have become, depending on whom you ask, more realistic, more complacent or more cynical. The most we dare imagine is less a cure than a lifetime managing HIV with meds -- for all HIVers worldwide.

Now, suddenly, out of the biostatistical blue, UCLA mathematicians have served up their own once-and-future dream of the end of AIDS. While not exactly graphic agitprop, this mathematical model, published in the August 1 Lancet, makes the case that global access to HIV meds could literally eradicate the pandemic from the planet. Talk about creative accounting!

The UCLA team of Jorge Velasco-Hernandez, Hayley Gershengorn and Sally Blower used a statistical technique dubbed “uncertainty analysis” to predict HAART’s effect on the transmission of HIV. Their calculations are all based on the self-evident premise that any epidemic will eventually end when the total number of people getting the disease is less than the total number giving it -- simple math. In practice, this means each HIVer must transmit the virus to less than one other person.

Taking as their sample San Francisco gay men, nearly one-third of whom are believed to have HIV, the math majors estimated that it would take 50 to 100 years to wipe out AIDS there. They calculated a best-case scenario based on three big ifs: that most HIVers get treatment (50 to 90 percent), that resistant virus is less infectious than wild-type, and that risky sex does not increase with treatment access. Also central to this happy ending is the assumption that despite the fact that HAART would give millions of HIVers much longer lives (in which to, er, transmit the virus), the meds also reduce an HIVer’s infectivity -- and, therefore, probably transmission rates -- by at least half.

Prevention experts were quick to dismiss all this as California dreamin’. “Despite being a statistician, I would argue against making public policy based on math modeling,” Stephen Gange of Johns Hopkins told Newsday’s Laurie Garrett. Why so skeptical? In the real world, said Gange, most HIVers are not on meds -- either because they don’t know they have the virus or because they don’t have the money.

The San Francisco Chronicle’s Sabin Russell called in local critics. Elliot Marseille of the city’s Institute for Health Policy Studies questioned the assumption that treatment reduces transmission. “Current data suggest most transmission occurs shortly after infection,” said Marseille, “but most treatment begins later on.” Doubting Tom Coates of UCSF’s Center for AIDS Prevention Studies weighed in with “All we have to go on is our experience. We’ve introduced antivirals, and infection rates have still gone up.”

Pipe-dream or AIDS’ E=MC2, the study puts a new spin on the long-running debate about whether resources should be devoted to treatment or prevention -- giving succor to both sides: If the model is right, treatment can eradicate AIDS, but only when coupled with effective risk reduction. "Treatment is prevention," said Blower -- hopefully.